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From: "Ron D' Eau Claire"
To:
Date: Fri, 11 Jan 2002 09:59:56 -0800
Subject: [Elecraft] Real World Antennas
Ed, W5EJ, wrote:
> dipole is 2.14db ABOVE an isotropic source. ...
I would
> hate to see beginners dissuaded from trying verticals without hearing an
> opposing opinion. In my experience, A GOOD vertical over
> a GOOD
> GROUND SYSTEM (salt water not required) does an excellent job! ...
> Example: I have a 40-meter dipole, approximately 1/4-wave above ground,
> (used to have one up 1/2-wave with very little difference noted)
> more or less broadside east and west and a Hy-Gain Hy-Tower
> vertical.
Hi,Ed!
This subject has been discussed at some length on this reflector in the
past, and probably will be again in the future. After all, it takes an
antenna to make a K2 or K1 get out!
Yes, a dipole has 2 db "gain" over an isotropic source (+2 dbi) in free
space, but the situation changes very quickly when you put it in a
real-world environment with the earth nearby.
At about 1/2 wavelength above the earth (assuming a 'typical' somewhat lossy
earth) the gain of a horizontal dipole over a vertical looks very impressive
on paper - something close to a full "S" unit (6 dB) at elevations normally
wanted for DX - and that is comparing a full half wave horizontal with a
full half wave vertical to avoid the issues of additional ground system
losses in a 1/4 wave vertical.
As you point out, such a difference is not always realized in practice for a
variety of reasons. Some of them are not always under our control.
Besides, while 5 or 6 dB sounds like a LOT of difference, it is easily
swamped by changing band conditions. Also, the "gain" of the dipole is off
the sides of the antenna, and that may not be the direction to the station
we are working. Off the ends of the horizontal, both antennas have very
similar performance.
There's a lot more to choosing an antenna than just plugging the numbers
into formulas or a simulator and looking for the desired pattern with the
highest gain. In my experience, it is a worthwhile place to start. When my
antennas don't behave on the air like they did on paper with a large error,
it's time to investigate how my real world antenna is different from the
paper version. That exercise usually yields some new insights.
Ron AC7AC
K2 # 1289
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Reply-To: "Don Wilhelm"
From: "Don Wilhelm"
To: , "Elecraft"
Subject: Re: [Elecraft] Power out on QRP records
Date: Sat, 12 Jan 2002 21:26:58 -0500
Tim,
You have the idea of putting the maximum power into an antenna right.
But, a properly designed antenna tuner should have little loss - this is
especially true for 'L-Network' tuner configurations such as those used in
the KAT1 and KAT2.
The real key is to minimize the loss - but a perfectly resonant antenna is
not necessarily the best answer.
The best efficiency is usually achieved by using a low loss feed-line -
especially if it is a rather long run. Open wire and ladder-line show
little loss even at high SWR, and the loss for RG-213 coax or even RG-8X at
less than 3:1 SWR is not bad either - of course losses in feedlines go up as
the frequency increases and the length increases, but we all knew that! I
guess the best efficiency would be with a zero length feedline, but then
radiation on low antennas gets absorbed in the nearby ground - so maybe K2
remote will allow us to put our transmitter at the antenna feedpoint
(Anyone know of an effective weatherproof housing?) Even if we are QRP, it
does not make much sense to me to use a lossy feedline unless the goal is a
lightweight setup for portable operation - physically large feedlines are
usually more efficient.
I could go on for hours on this - but I will end by saying that if the power
is going out of the transmitter, all that power - minus the feedline loss -
will be radiated by the antenna. (That is the conservation of energy
principle, and if anyone here wants more discussion off-list, I will happily
consent to all except for flames).
73,
Don Wilhelm - Wake Forest, NC W3FPR home page: http://www.qsl.net/w3fpr/
QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net
----- Original Message -----
> Hi folks -
> To continue from my earlier question re the K2 and external power
> meters: When heavy duty QRP types talk about power out and setting miles
> per milliwatt records - is it based on the power that goes to the ATU on
> a rig like the K2 or the K1? I guess the answer has to be yes - but if
> they are heavy in to competing they would be using that power more
> efficiently by bypassing a tuner and going to a perfectly resonant
> antenna - do I have the idea right? Thanks folks. 73/Tim Logan KB7OEX
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